Mythic items, currently, are items that take up an item slot in exchange for a bigger buff, similar to the two-set effect of monster helms. They come with a myriad of flavors, strengths, some with downsides that come along with those strengths.
But I have a suggestion: Minor Mythic Items, which come with their own unique item slot. Let me explain. These would be mythic items which count as mythic items, as you'd expect. You cannot equip one alongside a normal mythic item, but unlike normal mythic items, these minor mythics don't give a big effect in combat. If a minor mythic does have a combat effect, it would be small; a single smaller (but still relevant) buff, like minor berserk or empower, possibly its own unique effect with a combat trigger, but nothing game changing. It would add to a build slightly, or allow for a buff on a class that doesn't get the buff normally (like with empower as an example, not available to every class easily without Oaken). However since they do not take up a normal slot, they could be more unique in their designs or effects. For example, there could be a backpack mythic that goes in this slot; it looks like a backpack, and while you wear it, you have an increase in your inventory space. Or a peg leg mythic, which makes one of your legs a peg leg and gives extra damage to sea creatures, maomer, and pirates. It could also have more powerful effects in conjunction with stronger downsides.